The present invention relates to apparatus for manipulating stacked sheets, for example, X-ray films. More particularly, the invention relates to improvements in apparatus for converting a stack of overlapping sheets into a single file of discrete sheets. Still more particularly, the invention relates to improvements in apparatus for predictable singularization of stacked sheets having any one of a wide variety of widths, lengths and/or thicknesses.
It is already known to transfer successive outermost sheets of a stack of overlapping sheets from a first location to a second location where successive sheets enter a transporting device in such orientation that the plane of a sheet entering the transporting device is parallel or nearly parallel to the plane of the outermost sheet in the stack. It is also known to effect the transfer of successive outermost sheets by resort to suction cups which are rotatably mounted on a support and can be caused to perform angular movements under the action of a cam. Reference may be had to German Offenlegungsschrift No. 24 03 369 which discloses an apparatus wherein the suction cups are caused to attract the topmost sheet of a stack and thereupon perform an angular movement (in order to change the plane of the attracted portion of the topmost sheet and to thus separate the topmost sheet from the sheet therebelow) together with an upward movement (such upward movement also contributes to segregation of the topmost sheet from the next-to-the-topmost sheet) prior to reassuming their original orientation in order to move the singularized and partly lifted topmost sheet into a plane that is at least nearly parallel to the plane of the sheet therebelow (i.e., to the plane of the fresh topmost sheet).
A drawback of the just discussed conventional apparatus is that it can be used only for the singularization of sheets having a predetermined length and width. If the format of the sheet is changed, e.g., if a stack of relatively wide sheets is followed by a stack of narrower sheets, at least one of the suction cups does not engage the exposed side of the topmost sheet of the stack so that it draws air from the atmosphere and causes a reduction of suction (i.e., a rise of pressure) in each other suction cup because all of the suction cups are invariably connected to one and the same suction generating device. Furthermore, if the width of the sheets to be manipulated greatly exceeds the distance between the two outermost suction cups, the sheet material which extends laterally beyond the outermost suction cups flexes downwardly by gravity and prevents predictable introduction of the lifted sheet into the transporting device, e.g., into the nip of a pair of advancing rolls between which successive sheets advance on their way to the next processing station, for example, into a cassette for X-ray films. In other words, while the just discussed conventional apparatus is quite satisfactory for the manipulation of sheets having a predetermined format, any change in the format of sheets greatly reduces the reliability and utility of such apparatus and can render the apparatus useless for its intended purpose.